This project consists of continuing studies of the chemistry, structure, epidemiology, immunology and pathology of the human hepatitis viruses. The goal of such studies is the control of human viral hepatitis by application of the most appropriate methods, including active and passive immunization, chemotherapy and interdictation of spread of the viruses. Progress: hepatitis A viral antigen was purified from feces and used in newly developed sensitive assays for antibody to the antigen to study the seroepidemiology of hepatitis A virus infection in defined populations. The biophysical and biochemical characterization of hepatatis A viral antigen has begun, and studies of the immunopathology of hepatitis type A in non-human primates, using defined pools of virus, are in progress. An inactivated subunit vaccine for hepatitis type B has been developed and is undergoing extensive tests of safety and efficacy in chimpanzees. A third hepatitis B antigen, e antigen, is being characterized and its relationship to infectivity is being explored. Evidence that populations of hepatitis B viruses may contain defective interfering particles has been obtained, and its finding is being utilized in renewed attempts to isolate the virus. A newly recognized clinical syndrome, type non-A, non-B hepatitis, has been further defined and attempts to identify an etiologic agent intensified. BIBLIOGRAPHIC REFERENCES: Schaffner, F., Dienstag, J.L., Purcell, R.H., and Popper, H.: Ultrastructural studies of chimpanzee livers after infection with human hepatitis viruses A and B. Archives of Pathology 101: 113-117, 1977. Szmuness, W., Dienstag, J.L., Purcell, R.H., Prince, A.M., Stevens, C.E., and Levine, R.W.: Hepatitis type A: A seroepidemiologic study in 15 U.S. hemodialysis centers. Annals. Int. Med. 87: 8-12, 1977.